PR = Prevalence of Depression in Obese divided by Prevalence of Depression in Non-obese

A A+B PR = C C+D

Interpretation • PR=1.30 • Obese individuals were 30% more likely than non-obese individuals to have depression.

Advantage • No follow-up • May be quicker to conduct

Disadvantage • Time sequence/Temporality (what came first?) may be not intact: did the exposure really precede the outcome? • For exposures that do not change over time such as race or blood type, no problem.

What came first? Obese

Depression

Depression

Obese

PR vs. Prevalence OR • You can also calculate an odds ratio from a cross-sectional study. • Same formula as before: AD / BC • Logistic regression yields ORs. • Binomial regression will yield RR for a cohort study and PR for a crosssectional study